Genetic and plastic components of divergent male intersexual behavior in Misty lake/stream stickleback

The extent of variation in mating signals between environments can be an important determinant of reproductive isolation. We tested divergence in male courtship behavior between lake and stream three-spined stickleback (Gasterosteus aculeatus L.) in the Misty system, Vancouver Island. Presumably, genetically based divergence was assessed by comparing male behavior (aggressive, display, and nest activities) among Lake, Inlet, and Outlet ecotypes that were reared from fertilization to maturity in a common environment. Plastic components of behavior were assessed by comparing male behavior in presence of females from each of the 3 ecotypes. We found that Inlet males had less aggressive elements than Lake and Outlet males in their behavior, whereas Lake and Outlet males were similar in their behavior. We further found that males of all ecotypes performed less display and nest activities in the presence of Lake and Outlet than Inlet females and that the male mating behavior was influenced by the relative difference in male and female body sizes. We suggest that divergent selection has driven genetic divergence in aggressive behaviors, whereas other behavioral components respond more plastically to variation in female phenotype. We discuss the implications of these results for reproductive isolation.